Health: Indecent Exposure.(sunscreen)

indecent exposure

Some people don't use it enough; others rely on it too much. What scientists now know -- and many people don't -- about sunscreen.

fibers, causing sagging and wrinkling; and suppressing the skin's immune system. "Exposing the skin to UV radiation -- even at low doses that don't induce sunburn -- causes structural alteration to DNA," says Antony R. Young, deputy head of skin sciences at King's College in London. Human skin cells are adept at repairing themselves, but occasionally they fail. That's when mutant cells can multiply into cancer.

Sunscreen is defined as any product containing ingredients that can reflect, scatter, or absorb ultraviolet (UV) radiation. Sunburn is "overwhelmingly attributable" to UVB rays, wavelengths that make up only 0.5 percent of the ultraviolet spectrum, says Henry W. Lim, chairman of the department of dermatology at Henry Ford Health Systems in Detroit. In recent studies, researchers have observed that exposure to the more plentiful UVA radiation alone can damage DNA and inhibit the skin's immune reaction. "A prudent person would believe that UVA plays at least a role in melanoma, based on experimental and epidemiologic evidence," says Robert S. Stern, a professor of dermatology at Harvard Medical School. Thanks to years of exhortations to wear sunscreen, approximately 45 percent of Americans do so today. That's one reason why experts have been so puzzled and alarmed by the climbing rates of melanoma. Questions about sunscreen's protection against cancer began surfacing in the 1990s, when a few researchers published studies that found a troubling link between its use and elevated risks of melanoma. Then, in 1998, Marianne Berwick, an epidemiologist at Memorial Sloan-Kettering Cancer Center in New York City, turned the quiet academic debate into an open argument when she publicized her evaluation of ten studies. Two found that sunscreens appeared to prevent melanoma, three showed no effect, but half showed that risks of the cancer increased among those who wore sunscreen. Berwick's conclusion: "It's not safe to rely on sunscreen." Many dermatologists sharply disagreed. Recent analysis has found that most of those studies didn't consider an important point: Frequent wearers of sunscreen are often sun-sensitive -- "people who tend to have fair skin, burn easily, and be unable to tan," says Marta J. VanBeek, an assistant professor of dermatology at the University of Iowa in Iowa City who coauthored a review in Annals of Internal Medicine. Sun sensitivity is a known risk for melanoma. But surprisingly, even after researchers factored this in, sunscreen still didn't reveal a preventive effect. In all studies to date, it has shown no significant impact on lowering the risk of melanoma. Complicating the issue are additional flaws in the early research. Investigators asked people about their past tanning and sunscreen use, relying on their memories of a decade ago, or longer. Many of the subjects also wore sunscreen with no UVA protection. In more recent experiments in which researchers told groups of subjects to use products with UVA and UVB ...